Elastic Audio: The Art of Audio Compression & Expansion

Elastic audio. The myth, the hidden tool and treasure. Now, elastic audio can be all those things if used to its full potential. What is elastic audio you ask? Elastic audio’s definition simply lies within its name. It is basically the elasticity of an audio file or simply put, the compression and expansion of a file within Avid’s Pro Tools. This tool lives in Pro Tools as a very powerful “plug-in.” And I say “plug-in” simply for the fact that it does not exist in the Audiosuite and cannot be inserted on a track, like a traditional plug-in is. Elastic audio is used in a multitude of ways and has a lot of functionality to it. There are not only a lot of music applications for it but also can accomplish some really interesting sound design capabilities. Let’s get stretching!

In my opinion there are two methods in which we can use elastic audio. The first method is the simplest. To employ this method, all you have to do is hold down the Trim Tool and select the icon with the little clock on it (TCE Trim).

This method is good for stretching/compressing a few frames and simple audio files. It is the quickest method to employ in Pro Tools and I often use this to mildly stretch/compress files on a daily basis. However, anything more a few frames or a simple the audio file, the file will begin to show artifacts or digital distortion in your file. However, this method will not stretch or compress with files that have fades on them. It is best to remove them before you begin your time stretch.

The second method of elastic audio is where things get a touch more complicated and the capabilities to expand or compress audio increase tenfold. Here you can stretch or squeeze more complex sounds and complete more drastic expansions and compressions. To turn on this method of elastic audio, click on the little metronome looking icon on the left side of the track in the Edit View.

This action will then open up a drop-down box with four modes of elastic audio.

You can also turn elastic audio on in small view as well. (I like to work in small view, as medium view takes too long to scroll through when you’re working with more than a hundred tracks). Just click on the arrow in the upper left area of your track it will open up into these drop-down menus.

Once you click on one of the four modes of elastic audio for that track, Pro Tools will begin to process all the transients of that track and you will notice all the files turn grey if you’ve done it right. It may take a few minutes for Pro Tools to finish this task. It is important to note that it is best to only use elastic audio on the tracks that you wish to stretch or compress. Elastic audio is a very powerful tool and turning it on every track in a session will completely bog down your system.

So Which Mode Do You Choose?

Polyphonic Elastic Audio is probably the first place I start when I want to expand or compress a file. Polyphonic is used for the more complex audio files. What I mean by that is any audio file that is chordal or has a bevy of tones or variations going on. And generally, has the ability to stretch or squeeze most sounds with ease. When in doubt, try Polyphonic.

Here we have a complex sound effect that has a lot going on. I would definitely use the Polyphonic mode to address this file.

When stretched in Polyphonic mode, it is smooth and does not distort. If we were to use any other mode or the TCE method we would definitely not have arrived at this result.

Rhythmic Elastic Audio is primarily used for any and all music or rhythmic applications. What is really fantastic about this mode is the fact that it preserves the integrity of the beat over time.

Rhythmic or musical audio files in this mode are preserved and the continuity of the beat is intact over time.

Monophonic Elastic Audio is the simplest of the four modes. It is best used for basic hits, single notes and simplistic dialogue.

The last mode of elastic audio is Vari-speed. Now Vari-speed is pretty cool. It is essentially a very powerful Vari-fi plug-in, like the one found in the Audiosuite. However, the speed is directly related to pitch. So the more you compress the file, the higher pitched it will become and conversely, the more you expand a file the lower in pitch it will become.

Limitations

Now there are a few limitations to this powerful tool. In the digital age, although we can accomplish so much with audio and have so many tools to do so, we are limited by the amount of data each file contains. With that being said, for smoother and unartifacted audio, it is best to use more high fidelity audio files. You can expand or compress Lo-Fi audio files but the extent to which you can expand or compress that file is rather limited. Here is a classic Lo-Fi example being stretched only a couple frames (brownie points for anyone who can name that sound effect).

As you can see the file is very distorted and almost sounds unrecognizable.

Sound Design Purposes

Now this drastic distorted and artifacting can be used to create some really interesting effects. It tends to be more of a robotic sound in my opinion, so I’ve used the ability to stretch effects in this manner a number of times in more futuristic or alien designs. Here’s our Polyphonic example stretched way too much. When you’re file is turned to this reddish color, Pro Tools is basically warning you that you’ve taken your file too far. In Sound Design terms, it probably sounds pretty cool and you’ve probably reached your desired effect.

You can also take this sound design tool one step farther and warp individual portions of each file. If you change your track view to warp, Pro Tools will show you where all the transients are in your file.

Here you can drag these transients’ lines to achieve your desired effect or warp. You can also quantize these transients to the grid with the help of the quantize menu, which is accessed by pressing Option+0. It is important to note however, that you must have elastic audio turned on, on your track to access this view.

Elastic audio can be used in a multitude of ways. I encourage all sound designers/editors to give it a try but know its limitations. It is something that I can say with confidence, makes my workflow not only more efficient but cleaner. I can expand or compress a file in the matter of seconds and enable myself to focus more on the creative.